Radio frequency integrated circuits (RFICs) include increasing amounts of digital processing which, because radio frequency (RF) spectrum is a scarce resource, are required to operate in higher and higher frequency bands. For example, recently, frequency bands in the range 3 to 6 GHz are being deployed for the third generation partnership project (3GPP). In addition, target power consumption is continually being reduced. In response to these factors, RFICs are being implemented in deep complementary metal oxide semiconductor (CMOS) nodes using, for example, 28 nm technology.
Using deep CMOS nodes for RF design generates some problems due to the limited voltage handling of the transistors. One particular difficulty is low noise amplifier (LNA) design. Fast transistors are required in order to obtain low noise and high bandwidth in the LNA, and a high gain is required to suppress the noise of circuits following the LNA. Commonly, a resonator load is used at the LNA output, to enable high voltage gain and high output signal swing.
An increasing requirement is for multi-standard RFICs, particularly for mobile phones that support dual-call and/or WiFi. A User Equipment (UE) supporting multiple simultaneous 3GPP systems and/or WiFi might generate significant interference to its own receivers due to crosstalk between antennas. To reduce cost, it is desirable to minimise the filtering of signals at the input of a receiver, but this can lead to crosstalk that may cause high signal levels inside LNAs and damage them.
A particularly challenging scenario is a small cell base station deployed indoors. In this scenario, some UEs may be connected to an indoor system while other UEs are connected to an outdoor system, for example using an operator not available indoors, with all UEs potentially operating in the same frequency band. A UE connected to the outdoor system will transmit at a much higher output power than those connected to the indoor system, in order to be able to reach the outdoor base stations. This could cause high levels of interference in the LNAs of the indoor base station, sufficient to damage them. A UE connected to the outdoor system may act as a blocker to the indoor system and degrade all communication in that frequency band.
Another challenging scenario relates to beam forming radios, where preferably no filters are used before the LNA as a high number of antennas may be employed, for example in the order of a hundred. In this case high power out-of-band signals may enter the LNA and damage it.
There is a requirement for improvements in amplification.